The invention concerns an overhead cable transport installation, namely a lift with gondolas coupled in line to two parallel continuous motion suspension/haulage cables, by means of suspension bars hanging in the vertical symmetry plane of the two cables, and articulated on a carriage bearing at least one pair of detachable grips intended for connecting the carriage to both cables, in line, and disconnecting the gondolas in the terminals, by detachment of the grips, to allow for passenger embarkation and disembarkation, at null or reduced speed.
Gondola lifts of the type mentioned offer numerous advantages, particularly of simplicity, high capacity and ease of embarkation and disembarkation for the passengers.
The suspension is situated in the vertical symmetry plane of the two cables, and the fact that the gondolas rest on two cables instead of one provides them with a great lateral stability, as the side stresses, mainly wind, are transmitted to both cables.
A gondola of a known type (FR-A-1.249.949) has grips which clamp the cable from underneath, and the grip jaws fulfil the double function of supporting the gondola's weight and of locking it on the cable. The reliability of such grips is not absolute, as the weight tends to open the jaws. The grip dimensions, especially their protruding above and below the cable, prevent them from passing over the support rollers and under the pressure rollers, and it is therefore necessary to install guides that push the cable away from the rollers while the grip is passing over them, which is practically not possible in huge installations with high cable tension.
The purpose of this invention is to cope with these difficulties, and to allow a construction of twin suspension/haulage cable installations that would preserve the same advantages of simplicity as those of the single cable gondola lifts.
The installation according to the invention is characterized by the fact that every grip is made of a body that rests in coupled position on the upper face of the cable, slightly protruding upwards, and further of a pair of jaws protruding downwards from the body and enveloping the cable on both sides, the jaw ends coming level with or slightly lower than the lower face of the cable, with a view to facilitating the passing over or under the cable support rollers, and in such a manner that, inside the terminals, guide rollers push the cables away from each other so as to increase the clearance between them and allow for the disengagement of the carriage disconnected from the cables.
Still using conventional grips resting on the upper face of the cable, the difficulties occasioned by the passing over the rollers are solved, as well as operation safety problems, but the carriage still remains engaged between the cables, even after the jaws have been opened in the terminals. According to the invention, guide rollers increase the clearance between the cables in order to allow for the disengagement of the carriage and its travelling on to transfer rails independent of the cable lines.
The clearance between the cables results from a compromise between the need for maintaining the support structures' dimensions inside acceptable and controllable limits, and the necessity of maintaining between the cables enough space for the horizontal guiding rollers in the terminals, and for ensuring lateral stability. The optimal clearance is comprised between 25 and 100 cm, as near as possible to 75 cm. The cable diameter is comprised between 0.035 and 0.050 m, preferably about 0.042 m.
To derive the maximum benefit from the lateral stability provided by the twin support of the carriage, the gondola is fixed to the carriage by means of its suspension bar with only one possibility of motion, i.e. oscillating inside the vertical symmetry plane.
According to an improvement of the invention, the carriage bears two pairs of detachable grips; this means two grips for each cable, and these grips can be staggered with respect to each other in the direction of the carriage movement, or be set two by two in front of each other with a certain overlapping, for instance a coaxial lay-out of the springs. Both of the grips coupled to one cable are symmetrically placed on both sides of the cross symmetry axis of the carriage, which passes through the coupling points on the cables. The control of the opening and closing of the grips on entering or leaving the terminals may be common to all grips of one carriage, but it is however preferable, for reasons of safety and standardization, to provide for an individual control lever for every grip, that comes in contact with a rail or a fixed cam, in the usual manner, at the connecting and disconnecting points of the carriages. The control is then symmetrical with respect to the vertical symmetry plane of the cables, so as to prevent the action on the levers from throwing the carriage out of balance. A different control device may be envisaged. Every grip is then installed on the carriage on a rubber cushion allowing for a slight rotation of the grip with respect to the other one on the same cable, and of both grips on one cable with respect to the grips on the other cable, in order to prevent any warping of the carriage.
The four grips form a rigid junction quadrilateral between both cables, which of course move in phase. All of them have the same height symmetrically, and consequently they pass under parallel roller sets without generating dissymmetrical stresses that could put the carriage out of shape, or warp it. In the same way, the driving or braking devices at the entrance or exit of the terminals, or inside them, are always double and symmetrical.
According to an important feature of the invention, both cable lines offer a perfectly symmetrical friction, which means that the frictional resistances are identical for both cables, as a result of symmetrical trajectories and/or of braking devices applied to one of the cables.
In the drive terminal, each cable passes over an end pulley, both pulleys being identical and superposed. Both pulleys are driven through a differential device which applies the same pull to both cables. The differential may be mechanical, hydraulic or electric. The combined action of the differential, of the equality of the frictions and of the junction between both cables realized by the rigid quadrilaterals formed by the carriage grips, results in a synchronous movement preventing any staggering or slanting of the gondolas. Obviously, similar precautions are essential concerning the braking down of the pulleys, and, according to an additional development of the invention, the braking device interlocks both pulleys mandatorily. A very simple means consists of inserting the rims of both coaxial pulleys, which are very close to each other, between the jaws of the brake clamp, and the jaws will push the rims against each other when applying the brake. The use of a single brake clamp ensures an even distribution of the braking effort, and also a friction coupling of both pulleys, preventing any shifting. A brake lining with a certain elasticity can be adjusted to the outer circumference of each pulley.
Regarding the differential, it can be advantageously designed as an electrically working device, based on strictly identical outputs of both driving motors. In case of such a construction, the stresses to overcome are the same on both cable lines, the cable motion speed is the same, whatever the compared diameters of both drive pulleys, since the compared output is the product of the effort by the motion speed.
To achieve such an electric differential, provision must be made for a direct current supply source common to both motors with identical electric characteristics.
When both cable lines have equal efforts to overcome in line, if the mechanical efficiency of the machines is equal and if the motors are identical, the current voltages and intensities will be the same in each of both supply circuits of the motors, when the latter will be connected to the same direct current supply, and they will deliver the same output.
If on the other hand an exterior factor changes, particularly when the efforts to overcome in line are not equal, the motors will work in a dissymmetrical manner, with different voltages and/or intensities.
One of the essential advantages of this electric differential is that it reports any operation difference between the two lines--with respect to the initial state which may be slightly dissymmetrical.
Dials with different triggering points for control functions make it possible to know at any time the state of one of the lines with respect to the other, and to stop the installation automatically in case of disadjustment beyond a predefined value. This reporting and the control sequence make up an essential safety device.
In the cable tightening terminal, each cable goes over a loose guide pulley, and both pulleys are mounted on a mechanical, hydraulic or electric compensation bar that balances the tension in both of them. The pulleys can advantageously be staggered laterally with respect to the direction of the cables, by a distance corresponding to the clearance between the cables inside the terminal. The length distance between both pulleys offsets slight length differences between both cable lines.
In the terminals, the carriages are disconnected from the cables, and taken over by transfer rails running along the embarkation and disembarkation platforms. The carriages have four wheels rolling on the rails, and are driven either by gravity, or by a drive mechanism, for instance a chain with lugs. The wheels are mounted in pairs, in front of each other, and travel on two parallel rails in the straight sections. In the curves, there is only one rail left, on the inside of the curve, which facilitates shunting.
According to a prefered alternative of the invention, the carriage is put in between the two cables, the grips protruding outwards on both sides. After the opening of the grips and disconnection from the cables by an upward move of the carriage with respect to the cables, the latter are pushed away from each other in order to free a passage for the grips and to disengage the carriage downwards. The disengagement occurs on entering the terminal, when the carriage passes over to a clearing section. A symmetrical system at the terminal exit provides for re-engaging of the carriages on the cables.
The capacity of the gondolas, namely 12 up to 30 passengers, makes it possible to reduce the number of gondolas in service, and it is interesting to park the gondolas, or at least a sufficient number of them to cope with normal traffic, on the transfer rails, the gondolas leaving only on request.
Each of the suspension/haulage cables passes at every tower over a balancing unit bearing either support rollers or pressure rollers. Both identical balancing units are perfectly symmetrical, and their main axles are strictly in front of each other. The reversed U supports of these axles are for instance centered in front of each other on the same boring machine at the works. The reversed U supports allow for free passage of the carriages between the outriggers. The short distance between the cables, of about 75 cm, ensures a sufficient stiffness with usual structures. In order to maintain a perfect symmetry of the balancing units, their elements are connected to each other by reversed U's placed at the entrance of every element, the entrance being defined with respect to the direction of the cables' motion.
The disposition of the invention which suppresses any side swinging on passing the towers allows for the use of support rollers whose inner flanges with respect to the line have a larger diameter in order to achieve a very efficient anti-derail device.
According to a realization alternative, the grips are turned towards the inside, the U-shaped carriage enveloping both cables. The overall dimensions of the carriage are larger, but the balancing unit supports are simpler and comprise only a cross bar supporting a unit at each of its ends. The disengagement of the carriage requires a squeezing of both cables.